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Journal of Paleontology 91(1):179–193
but the summits of the three most anterior lophs are so badly broken that cusps cannot be distinguished. This specimen has four lophs and a nodular talon. The posttrites are bicuspid, with small adaxial conelets. In these features, the Jining specimen resembles the Tha ChangM3, PRY200. In particular, the bicuspid nature of the posttrite and the presence of small adaxial conelets can be clearly recognized in the fourth loph of PRY200. However, the fourth loph of PRY200 is better developed than that of the Jining specimen. In addition, the pretrite of the fourth loph of the Jining specimen has two subequal larger mammillae separated by two smaller squeezed ones (see Tobien et al., 1988, p. 151, fig. 42), while the main cone of the Tha Chang specimen is large and transversely elongate with small one adaxial conelets presented (Figs. 2, 4.1). The zygodont crests of the Jining specimen are better developed than in the Tha Chang M3, and the molar is shorter (Tables 1, 3; Fig. 5.2). Miomastodon tongxinensis Chen, 1978 is represented by
an m3 (IVPP-V5584) and an M3 (IVPP-V5585), from Gujiaz- huangzi, Tongxin, Ningxia. The anterior loph of the upper third molar is strongly worn. The third loph has a small adaxial conelet and a strong anterior conule, but no posterior conule is present. The first and third posttrite half lophs have oblique, oppositely oriented long axes, while the second one is normal to the tooth midline. An antero-external cingulum is present. The pretrite side of the fourth loph has an abaxial main cone and a smaller adaxial conelet. In the above characters, the Tongxin M3 resembles the Tha ChangM3, PRY200. However, the Tongxin M3differs from the Tha Chang M3 in that the posttrite half lophs are bicuspid, zygodont crests are present only in the first and second lophs, and the fourth loph is the narrowest one. The lower third molar is similar to the ThaChang m3 NRRU-TKK001 in that the third and fourth lophids bear small adaxial conelets, and the upper and lowermolars fromTongxin are similar in size to their counterparts from Tha Chang (Tables 1–3; Fig. 5.1, 5.2). Nevertheless, the pretrite and posttrite of the fourth loph(id)s are bicuspid in both Tongxin molars, whereas the posttrite fourth loph is tricuspid in the Tha Chang specimens. Zygolophodon chinjiensis was named by Osborn (1929) as
Serridentinus chinjiensis. The type specimen (AMNH 19447), a right upper third molar (Osborn, 1929, p. 4, fig. 5), bears four ridges and a posterior cingulum. The anterior lophs are each divided into many conelets. We cannot determine whether this character is present in the Tha ChangM3 because of deep wear. However, the fourth loph has a tricuspid posttrite side, and a bicuspid pretrite side. The adaxial conelets are smaller than the main cone, as in the Tha ChangM3. The zygodont crests, crescentoids and lateral cingula of Z. chinjiensis are much stronger than those of the Tha Chang M3. The type specimen of Z. chinjiensis is much wider and a bit longer than the Tha ChangM3 (Table 1; Fig. 5.2). Z. chinjiensis from China was described by Chow and
Chang (1978), based on two specimens of M3 (IVPP-V4688.1 and IVPP-V4688.2) from the upper Miocene of Xiaolongtan coal mine, Kaiyuan, Yunnan. These Chinese specimens each bear four lophs with posteriorcingulum and have two conelets on the pretrite side. The third and fourth posttrites are similar to the Tha Chang M3 in being tricuspid, but the main cone of the fourth loph pretrite is less transversely elongated than in the Tha Chang M3. The crescentoids are stronger and the size is larger than in the Tha Chang M3 (Tables 1, 3; Fig. 5.2).
Zygolophodon lufengensis from the upper Miocene
(Biasatti et al., 2012) of Shihuiba, Lufeng, Yunnan, was described by Zhang (1982). The holotype, left lower m3 (Zhang, 1982, pl. 1, fig. 1), bears four lophids with small a posterior cingulum, and the antero–external and pretrite cingula are quite strong. Zygodont crests are visible on the first and second lophids. The conelets on both the pretrite and posttrite half lophids are small. Hence, this specimen can be referred to Zygolophodon gobiensis, (i.e., Tobien et al., 1988) and is similar to the Tha Chang specimens. In addition, the Lufeng m3 is similar in molar size to Miomastodon tongxinensis and the Tha Chang specimen, but the M3 of Lufeng specimen is larger than both Tongxin and Tha Chang specimens. The m3 of Z. lufengensis shows an advanced character state not seen in M. tongxinensis and Z. gobiensis, in that the transverse lophids are rather oblique; however, it is also present in the Tha Chang m3 (Tables 1–3; Fig. 5.1, 5.2). However, Tobien et al. (1988) synonymized many
Chinese zygodont proboscideans with Zygolophodon gobiensis, including Zygolophodon gromovae Dubrovo, 1974, Z.(Turicius) nemonguensis Chow and Chang, 1961, Z. nemonguensis Yan, 1979 (M3, IVPP2487), Z. jiningensis Chow and Chang, 1974 (M3, IVPP-5156), Z. chinjiensis Chow and Chang, 1978, Miomastodon tongxiensis Chen, 1978, fragments of M1, IVPP-4685.7 and 4685.8, of Gomphotherium xiaolongtanensis Chow and Chang, 1978, from the upperMiocene of Xiaolongtan coal mine, Kaiyuan, Yunnan. In addition, Tobien et al. (1988) transferred some species of
Zygolophodon to Mammut borsoni, including an upper D4 (IVPP-V4685) of Zygolophodon sp. from the lower or middle Pliocene of Anle, Huoxian, Shanxi; M3 and m3 (IVPP-VM867 and IVPP-V2485) of Z. shansiensis Chowand Chang, 1961 and M3 (IVPP-V2488) of Zygolophodon sp. (Chow and Chang, 1961) from the upper Pliocene or lower Pleistocene of the Yushe Basin, Shanxi; M2 (IVPP-V4689) of Zygolophodon sp. (Chow et al., 1978) from the Pliocene of Zhaotong, Yunnan. All of the above taxa and specimens are larger in terms of molar size than the Tha Chang specimens, as well as having stronger zygodont crests and lophids that are more obliquely aligned to the long axes of the teeth (Tables 1–3; Fig. 5.1, 5.2). Zygolophodon metachinjiensis Osborn, 1929 is represented
by a right hemimandible with m2 and m3 (AMNH 19414) from the middle Miocene of lower Chinji Formation, Chinji, Pakistan. The m3 has four lophids, and a low posterior cingulum consisting of many accessories this cingulum. Molar is subhypsodont (75 mm height) and has no cement, and the summits of the lophids each consist of four to five conelets. Tobien (1972) allocated the holotype, lower m2 and m3, of Z. metachinjiensis to Gomphotherium by used the character of subhypsodonty and relatively large size of m3 that were mentioned by Osborn (1936, p.456). However, there are a few details in this holotype. In 1983, Tassy synonymized the upper M3 of Z. chinjiensis and lower m2 and m3 of Z. metachinjiensis (Osborn, 1929) to Z. metachinjiensis. In this case, after considering the figures of Osborn (1929, figs. 4, 5, 5A and A1) and new material of Tassy (1983a, pl. 2, fig. 2), Tobien et al. (1988) suggested the relations are narrow in their proportions, like the lower and upper second and third molars of Z. gobiensis. The pretrite conelets are rather small in Z. metachinjiensis,
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